The various embodiments of the present invention are generally directed to self-hardening calcium phosphate-containing and/or calcium-containing cement compositions. The compositions may be used to form pastes for bone and tooth restoration and similar applications, where the paste will harden within a desired time after being delivered to a repair site.
Most conventional calcium phosphate cements are mixed with an aqueous solution immediately before application. In the clinical situation, the ability of the surgeon to properly mix the cement and then place the cement paste in the defect within the prescribed time is a crucial factor in achieving optimum results.
A self-hardening calcium phosphate cement (“CPC”), consisting of tetracalcium phosphate (Ca4(PO4)2O, also referred to as “TTCP”) and dicalcium phosphate anhydrous (CaHPO4, also referred to as “DCPA”), has been shown in clinical studies to be efficacious for repairing bone defects. The hardening time of such conventional cements is as long as about 30 minutes with water, although hardening time can be shortened if a phosphate solution is used as the cement liquid. Hydroxyapatite (Ca5(PO4)3OH, also referred to as “HA”) is formed as the product. More recently, additional CPCs that do not contain TTCP, e.g., α-tricalcium phosphate (α-Ca3(PO4)2, also referred to as “α-TCP”) and CaCO3 or DCPA and Ca(OH)2, have also been developed. These cements may harden in about 10 minutes when a phosphate solution is used as the cement liquid. They also form hydroxyapatite (“HA”) as the final product.
A premixed CPC paste containing the TTCP and DCPA powders and glycerol as the cement liquid has been used for root canal filling and sealing by injection techniques. The cement paste was found to be stable in a syringe but hardened only after being delivered into the root canal where it became exposed to water from the surrounding tissues. Because the cement paste was injected into a confined area, there was little concern of disintegration of the paste due to washout. Although the premixed CPC was shown to have improved biocompatibility with periapical bone tissue than a number of conventional root canal filling or sealing materials, the premixed CPC-glycerol paste did not exhibit a good washout resistance when it was applied to an open wet field.
There remains a need for premixed cement pastes that are stable in the package, are resistant to washout, and will harden only after being deposited at the site of the defect but, once placed, will then harden within a predetermined time.